This invention relates generally to microwave devices, and particularly to a waveguide-to-microstrip line coupling arrangement and a microwave frequency converter including such a coupling arrangement.
Microwave semiconductor devices using GaAs FETs have been developed recently, and microstrip integrated circuits (MICs) are widely used. In a microwave receiver to be connected to a parabolic antenna, such as in an SHF receiver used for receiving satellite broadcasting waves, a radio frequency (RF) signal fed from a parabolic antenna has to be fed from a waveguide to a microstrip line. According to a conventional waveguide-to-microstrip line coupling arrangement, a ridge waveguide is used and therefore the structure is complex. Furthermore, since the waveguide is short-circuited to the microstrip line via the ridge waveguide in connection with d.c., a blocking circuit is required at an input of an MIC when the MIC comprises active devices. As a result, insertion loss in increased or noise figure is increased. Furthermore, when it is intended to keep the coupling between the waveguide and the microstrip line throughout a wide frequency range, it is necessary to employ a number of stages of ridge waveguides which results in increase in size and insertion loss.